The present invention relates to a decoding device for decoding pulse code modulation (PCM) audio data in a satellite broadcasting receiver, and more particularly to a circuit capable of muting an audio signal upon determining the presence of scrambling during the decoding process of the received PCM audio data.
Generally, scrambling signifies that a frequency position 15 is selected while synchronization is adjusted between counterpart devices in the communication system. In a scrambling communication system used for commercial satellite broadcast, a transmitting side limits the communication of a receiving side. Namely, a satellite broadcasting receiver subscriber must pay a fee in order to receive the scrambled signal. The scrambled signal sent from the transmitting side is reproduced at the receiving side by using descrambling techniques. In this case, a charged flag signal for giving notice that a transmitting signal is scrambled is inserted in a frame of the PCM audio data.
When receiving the scrambled signal through a satellite broadcasting receiver, an image signal is displayed in non-standard form and noise interferes with the audio signal. That is, whereas general audio data received from the satellite broadcasting receiver is reproduced with good tone quality, the scrambled audio data is reproduced with a tone harsh to the ear because of the noise. Therefore, if the scrambled PCM audio data is received by the satellite broadcasting receiver, it would be beneficial to check whether scrambling is present, and, if so, to mute the audio signal upon detection of the scramble.